1. Field of the Invention
The present invention relates to a substrate cleaning apparatus, and more particularly to a substrate cleaning apparatus suitable for cleaning a substrate which requires a high level of cleanliness, such as a semiconductor wafer, a glass substrate, a liquid crystal panel, etc.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnection is photolithography. Though the photolithographic process can form interconnections that are spaced by a distance of at most 0.5 .mu.m, it requires that surface on which pattern images are to be focused by a stepper is as flat as possible because the depth of focus of the optical system is relatively small. If particles larger than the distance between adjacent interconnections are present on a substrate, then they tend to cause a short circuit between the interconnections. Therefore, it is important that the substrate is cleaned as well as planarized in its fabrication process. The same processing requirements apply to other substrates including glass substrates, liquid crystal panels, etc. In view of these requirements, there has been a demand for cleaning techniques for removing smaller particles, i.e., submicrons, from semiconductor substrates or the like.
According to a known process of cleaning a polished semiconductor substrate to a high level of cleanliness, the surface to be cleaned of the substrate is scrubbed by a cleaning member such as a brush or a sponge that is rubbed against the substrate (primary cleaning), and then a stream of water under high pressure, i.e., a high-speed jet of water, is ejected toward the substrate to produce air bubbles due to cavitation to clean the substrate (secondary cleaning).
FIG. 9A of the accompanying drawings shows a conventional general arrangement of a substrate cleaning apparatus for use in scrubbing a substrate. The substrate cleaning apparatus has a plurality of upstanding substrate-holding rollers 100 openably and closably disposed around a substrate W. The substrate-holding rollers 100 has holding grooves 102 defined in upper ends thereof for holding the edge of the substrate W and rotating the substrate W upon rotation of the rollers 100. As shown in FIG. 9B of the accompanying drawings, a pair of cleaning devices 108 is disposed in sandwiching relationship to the substrate W. The cleaning devices 108 are rotatable about respective axes thereof and movable into and out of contact with the substrate W. Each of the cleaning devices 108 comprises a solid shaft 104 and a cleaning member 106 in the form of a tubular sponge, brush, or the like disposed on the surface of the solid shaft 104. As shown in FIG. 9C of the accompanying drawings, nozzles 110 which supply a cleaning liquid, pure water, or the like to the face and back of the substrate W are provided.
While the substrate W is being held and rotated by the rollers 100, the cleaning liquid is supplied from the nozzles 110 to the face and back of the substrate W, and the cleaning members 106 are rubbed against the substrate W to scrub the substrate W (primary cleaning) for thereby removing deposits of an abrasive liquid, a polishing residue, etc. from the entire face and back of the substrate W.
Since the scrubbing process is carried out while the cleaning members 106 are being held in contact with the substrate W, the contamination of the cleaning members 106 themselves governs the cleaning effect. If the contamination of the cleaning members 106 progresses, then the contaminant attached to the cleaning members 106 tends to contaminate the substrate W. Therefore, as shown in FIG. 9C, a cleaning tank 114 filled with a cleaning liquid 112 is disposed in a retracted position of the cleaning devices 108, and each of the cleaning devices 108 is cleaned by being dipped and rotated in the cleaning liquid 112 in the cleaning tank 114.